Communications techniques enable digital signals to be sent and received at very high bit rates. These communications techniques, which are known generically as digital subscriber line (DSL) or xDSL, include, by way of example, asymmetric digital subscriber line (ADSL) and its derivatives ADSL2, ADSL2plus, symmetric digital subscriber line (SDSL), or indeed very high bit rate digital subscriber line (VDSL), and VDSL2.
In the context of sustainable development, it is desirable to diminish the electricity consumption associated with communications lines.
The standard ITU-T G.992.3 describes a so-called “L2” mode for reducing the power of an ADSL2 line when there is a reduction in traffic. More precisely, that mode enables the power with which a down signal is sent over a digital subscriber line to be reduced, i.e. a signal going from the exchange to the client equipment.
An ADSL2 line has a certain number of carriers for transporting data. Some of the carriers are reserved for transporting data in the up direction (from the client to the exchange). Other carriers are reserved for transporting data in the down direction (from the exchange to the client).
When there is a large amount of traffic (mode L0), each carrier has a predetermined power as is needed for transporting the data.
On changing to L2 mode, the power of each carrier is diminished by a predetermined number of decibels. A decrease of 10 decibels (dB) may for example give rise to an energy saving of 500 milliwatts (mW) per ADSL2 line.
Nevertheless, that mode leads to very strong variations in noise power on neighboring lines. Those variations have the consequence of numerous disturbances such as signal losses, high error rates, resynchronization.
There therefore exists a need for a low consumption mode that does not disturb neighboring lines.